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Abstract Population demographic changes, alongside landscape, geographic and climate heterogeneity, can influence the timing, stability and extent of introgression where species hybridise. Thus, quantifying interactions across diverged lineages, and the relative contributions of interspecific genetic exchange and selection to divergence at the genome‐wide level is needed to better understand the drivers of hybrid zone formation and maintenance. We used seven latitudinally arrayed transects to quantify the contributions of climate, geography and landscape features to broad patterns of genetic structure across the hybrid zone ofPopulus trichocarpaandP. balsamiferaand evaluated the demographic context of hybridisation over time. We found genetic structure differed among the seven transects. While ancestry was structured by climate, landscape features influenced gene flow dynamics. Demographic models indicated a secondary contact event may have influenced contemporary hybrid zone formation with the origin of a putative hybrid lineage that inhabits regions with higher aridity than either of the ancestral groups. Phylogenetic relationships based on chloroplast genomes support the origin of this hybrid lineage inferred from demographic models based on the nuclear data. Our results point towards the importance of climate and landscape patterns in structuring the contact zones betweenP. trichocarpaandP. balsamiferaand emphasise the value whole genome sequencing can have to advancing our understanding of how neutral processes influence divergence across space and time.
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This content will become publicly available on July 25, 2026
Climate and hybridization shape stomatal trait evolution in Populus
Abstract Stomata play a critical role in regulating plant responses to climate. Where sister species differ in stomatal traits, interspecific gene flow can influence the evolutionary trajectory of trait variation, with consequences to adaptation.Leveraging six latitudinally-distributed transects spanning the natural hybrid zone betweenPopulus trichocarpa–P. balsamifera, we used whole genome resequencing and replicate common garden experiments to test the role that interspecific gene flow and selection play to stomatal trait evolution.While species-specific differences in the distribution of stomata persist betweenP. balsamiferaandP. trichocarpa, hybrids on average resembledP. trichocarpa. Admixture mapping identified several candidate genes associated with stomatal trait variation in hybrids includingTWIST, a homolog ofSPEECHLESSinArabidopsis, that initiates stomatal development via asymmetric cell divisions. Geographic clines revealed candidate genes deviating from genome-wide average patterns of introgression, suggesting restricted gene flow and the maintenance of adaptive differences. Climate associations, particularly with precipitation, indicated selection shapes local ancestry at candidate genes across transects.These results highlight the role of climate in shaping stomatal trait evolution inPopulusand demonstrate how interspecific gene flow creates novel genetic combinations that may enhance adaptive potential in changing environments.
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- Award ID(s):
- 1856450
- PAR ID:
- 10633509
- Publisher / Repository:
- bioRxiv
- Date Published:
- Format(s):
- Medium: X
- Institution:
- bioRxiv
- Sponsoring Org:
- National Science Foundation
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